Role of alpha7-nicotinic acetylcholine receptors in tetanic stimulation-induced gamma oscillations in rat hippocampal slices.

Hippocampal gamma oscillations, as a form of neuronal network synchronization, are speculated to be associated with learning, memory and attention. Nicotinic acetylcholine receptor alpha7 subtypes (alpha7-nAChRs) are highly expressed in hippocampal neurons and play important roles in modulating neuronal function, synaptic plasticity, learning and memory. However, little is known about the role of alpha7-nAChRs in hippocampal gamma oscillations. Here, we examined the effects of selective alpha7- and non-alpha7-nAChR antagonists on tetanic gamma oscillations in rat hippocampal slices. We found that brief tetanic stimulation-induced gamma oscillations (30-80 Hz) and pharmacological blockade of alpha7-nAChRs using the relatively selective alpha7-nAChR antagonists, methyllycaconitine (10 or 100 nM) or alpha-bungarotoxin (10 nM), significantly reduced the frequency spectrum power, the number of spikes, and burst duration of evoked gamma oscillations. Neither mecamylamine nor dihydro-beta-erythroidine, which are selective antagonists of non-alpha7-nAChRs, demonstrated significant effects on tetanic gamma oscillations. Nicotine exposure promotes hippocampal gamma oscillations in a methyllycaconitine-sensitive manner. It is concluded that alpha7-nAChRs in hippocampal slices play important roles in regulation of gamma oscillations, thus potentially helping to explain roles of nAChRs in cognitive functions such as learning, memory and attention.